NL2025353B1

NL2025353B1 - Conveyor Belt for a Sheet Transport System

Info

Publication number: NL2025353B1
Application number: NL2025353A
Authority: NL
Inventors: Rietbergen Mark; M Kuypers Hermanus
Original assignee: Canon Production Printing Holding Bv
Priority date: 2020-04-16
Filing date: 2020-04-16
Publication date: 2021-10-26
Also published as: DE102021109005A1

Abstract

A conveyor belt (10) for a sheet transport system, wherein the belt has a weld seam (16) extending across the belt in a seam direction (8) inclined relative to a width 5 direction (VV) of the belt (10), and the belt has a pattern of through-holes (18) arranged in a regular lattice, the lattice having a number of axes (a1, a2, a3, a4) on which the through-holes (18) are aligned, and having a lattice main direction (M) defined as the direction of the axis (a1) for which a deviation from the width direction (W) is smallest, wherein in that the seam direction (8) and the lattice main direction (M) are oppositely 10 inclined relative to the width direction (VV). (Fig. 1)

Description

Conveyor Belt for a Sheet Transport System The invention relates to a conveyor belt for a sheet transport system, wherein the belt has a weld seam extending across the belt in a seam direction inclined relative to a width direction of the belt, and the belt has a pattern of through-holes arranged in a regular lattice, the lattice having a number of axes on which the through-holes are aligned, and having a lattice main direction defined as the direction of the axis for which a deviation from the width direction is smallest.

A conveyor belt of this type has been described in US 2016193855 A1. In a sheet transport system of, e.g., a printer, such a conveyor belt is configured as an endless belt trained around two rollers and driven to convey print media sheets through processing stages of the printer. In order for the sheets to be held in stable positions on the belt, a suction box is disposed underneath the upper run of the belt, and the belt is perforated by through-holes that are finely distributed over the area of the belt, so that ambient air is drawn into the suction box through the through-holes of the belt, thereby to attract the sheets to the belt.

The endless belt is formed from an elongated piece of web material the opposite ends of which have been joined together at the weld seam. In order to assure a smooth running behavior of the belt when the belt seam runs over a roller or through a nip between two rollers, it is convenient to cut the web into the separate pieces of web material along cut lines that are inclined relative to the width direction of the web, so that, consequently, the weld seam of the endless belt has also a seam direction that is inclined relative to the width direction of the belt. The angle of inclination of the seam direction is typically in the order of magnitude of 1 to 10%. A larger angle of inclination would increase the risk that the endless belt is warped at the weld seam when the belt is under tension. In the known conveyer belt, the through-holes are arranged in a regular lattice having a lattice main direction that is parallel to the seam direction. Thus, the through-holes are aligned in straight rows that extend in parallel with the weld seam and are separated by certain spacings in the direction normal to the lattice main direction. Consequently, if the width of the weld seam is smaller than the interspace between two adjacent rows of through-holes, it is possible to position the weld seam such that it is entirely accommodated in the interspace, so that none of the through-holes will be blocked by the weld seam.

However, this known design imposes limits on the width of the weld seam in relation to the spacings between the rows of through-holes. If the weld seam is required to have a larger width, in order to assure a sufficient strength of the welded joint, and/or the through-holes are required to form a very fine pattern in order to assure a uniform attraction of the sheets, this limit can no more be respected, and an entire row of through-holes will become blocked. If an edge of a media sheet happens to be positioned on such a blocked row of through-holes, the edge of the sheet might bend upwards, and this may cause damage, for example due to a collision of the upwardly bent sheet edge with an ink jet print head of the printer.

Even if the width of the weld seam can be made smaller than the interspace between the rows of through-holes, it is cumbersome to accurately position the cut lines, along which the web is cut, relative to the rows of through-holes.

It is an object of the invention to improve the reliability with which sheets can be held in a flat condition on the conveyer belt.

In order to achieve this object, the conveyer belt according to the invention is characterized by the feature that the seam direction and the lattice main direction are oppositely inclined relative to the width direction.

Thus, in a typical configuration of the conveyor belt according to the invention, the weld seam does cross at least one row of through-holes, so that a number of these through- holes will be blocked. However, since the seam direction and the lattice main direction deviate from the width direction of the belt in opposite directions, the angle formed between the weld seam and the rows of nozzles is larger than the angle of inclination of the weld seam and larger than the angle of inclination of the lattice main direction. Due to this large angle, the number of adjacent through-holes that will be blocked by the weld seam where the weld seam crosses the row of through-holes will only be relatively small. Thus, if an edge of a sheet happens to be positioned such that it crosses the weld seam, the segment of the edge that is not properly attracted to the belt will only be relatively short, so that the edge is prevented from curling upwards in this short segment. As a consequence, the sheets can reliably be held in a flat condition on the belt even in a worst-case scenario. Moreover, the limitation concerning the admissible width of the weld seam and the spacings between the rows of through-holes is eliminated, so that it is possible to provide conveyer belts with a broad weld seam which can withstand large tensional forces and/or to provide conveyer belts with very fine patterns of through-holes for uniformly attracting particularly limp sheets. The invention also facilitates the manufacturing process for the conveyer belts, because it is sufficient to adjust the angle of inclination of the cut line but it is not necessary to precisely position the cut line relative to the lattice of through-holes. More specific optional features of the invention are indicated in the dependent claims. In one embodiment, the regular lattice of the through-holes is a tessellation of the area of the belt with rhomboids or isosceles triangles. The angle of inclination of the seam direction relative to the width direction may be 10° or smaller. Similarly, the angle of inclination between the lattice main direction and the width direction may be 10° or smaller.

In one embodiment, the weld seam may have a width that is a larger than the width of an interspace between adjacent rows of through-holes that extend in the lattice main direction. The invention also provides a method of manufacturing a conveyor belt, comprising the steps of: - providing an endless web material having a pattern of through-holes arranged in a regular lattice, the lattice having a number of axes on which the through-holes are aligned, and having a lattice main direction defined as the direction of the axis for which a deviation from the width direction is smallest;

- cutting the endless web into pieces along cut lines that are inclined relative to the width direction of the web; and - welding opposite ends of each cut piece together, thereby to form the endless conveyor belt having a weld seam, characterized by the steps of: - first detecting the lattice main direction of the web; - and then adjusting the direction of a cutting tool such that the cut lines and the lattice main direction are oppositely inclined relative to the width direction. Embodiment examples will now be described in conjunction with the drawings, wherein: Fig. 1 is a schematic view of a part of a perforated endless conveyor belt having a weld seam; Fig. 2 is a view analogous to Fig. 1, illustrating an effect of different inclinations of the weld seam; Fig. 3 is another view similar to Fig. 2, illustrating the effect of the different inclinations in a different scenario; Fig. 4 is a diagram illustrating essential steps of a method of manufacturing the conveyor belt; and Fig. 5 is a longitudinal section of the endless conveyor belt.

As is shown in Fig. 1, an endless conveyor belt 10 is arranged to move in a longitudinal direction A of the belt, which longitudinal direction is parallel to edges 12, 14 of the belt. A width direction W of the belt is the direction orthogonal to the longitudinal direction A. The conveyor belt 10 has a weld seam 16 where opposite ends of a piece of web material that constitutes the belt have been welded together with some overlap, so that the weld seam has a width b. The weld seam 16 extends in a seam direction S which is inclined relative to the width direction W, so that the weld seam forms an angle B with the width direction.

The conveyor belt 10 is perforated by evenly distributed through-holes 18 which are arranged to form a regular lattice.

The lattice has a number of axes a1, a2, a3 and a4 along which the through-holes 18 are aligned with uniform spacings.

None of the axes al, a2, a3 and a4 is parallel to the width direction W.

The axis a1, for which the angular 5 deviation from the width direction W is smallest, defines a lattice main axis M which forms an angle -¢ with the width direction W.

The minus-sign for ¢ indicates that the seam direction S and the lattice main direction M are inclined relative to the width direction W in opposite directions, i.e.

S is inclined relative to W in counterclock sense by a positive angle B, whereas M is inclined relative to W in clock sense by a negative angle -¢. Consequently, an angle between the edge 14 of the belt and the seam direction S (in counterclock sense) is 90° + B, whereas an angle between the edge 14 and the lattice main direction M is 90° - ¢. It is a characteristic of the conveyor belt 10 disclosed here that one of the angles which an edge of the belt forms with the seam direction S and the lattice main direction M is larger than 90° whereas the other of these angles is smaller than 90°. In the example shown, the regular lattice formed by the through-holes 18 is a tessellation of the area of the belt 10 with isosceles triangles.

Consequently, the axes a1 and a2 form an angle of 60°, the axes a2 and a4 also form an angle of 60°, and the axes al and a3 are orthogonal to one another.

The through-holes 18 are arranged along the axis a1 with a uniform spacing s1. Analogously, the spacings of the through-holes along the axes a2, a3 and a4 can be designated as s2, s3 and s4, respectively.

In the particular lattice shown here, the relation between these spacings is: 82 = s4 = 31 83 =3 x s1

The parallel rows of through-holes 18 that are aligned on the axes a1 have a spacing d which, in this particular lattice, is equal to %4 s3. Fig. 2 schematically illustrates a situation in which a media sheet (of which only a leading edge 20 has been shown) has been placed on the conveyor belt 10 in such a position that the leading edge 20 crosses the weld seam 16. The rows of through-holes 18 that are aligned on the lattice axes a1 (extending in the lattice main direction M) are almost parallel with the leading edge 20. Thus, any segment of the leading edge 20 is framed between two adjacent rows of through-holes, one row being covered by the media sheet whereas the holes in the other row are not.

In a sheet transport system, the conveyor belt 10 moves in the direction A over a suction box 22 (Fig. 5) which is open at its top side, so that air is drawn in through the through-holes 18 of the belt. The purpose of this suction mechanism is to attract the media sheets to the belt, so that the media sheets keep their positions on the belt and are safely held in a perfectly flat state. In particular, if the sheets (e.g. paper sheets) tend to cockle, it is important that the edge portions of the sheets are reliably pinned to the surface of the belt. In the situation shown in Fig. 2, this is the job of the row of through-holes 18 that is adjacent to the leading edge 20 but is already covered by the sheet (on the right side of the leading edge 20 in Fig. 2, i.e. on the trailing side in the transport direction A). However, as is shown in Fig. 1, the leading edge 20 has a certain segment of a length L1 in which the through-holes 18 in the nearest row are blocked by the weld seam 16, so that the leading edge cannot be attracted to the belt here. Obviously, in order to keep media sheets flat, the objective is to make the length L1 or, equivalently, the number of blocked through-holes 18 as small as possible. In view of this, it turns out to be advantageous that the seam direction S and the lattice main direction M are inclined relative to the width direction W in opposite directions. For comparison, Fig. 2 also simulates the situation for a weld seam 16’ which has the same width b and the same angle of inclination relative to the width direction, but with an opposite sense of the inclination, i.e. with the seam direction being inclined in the same direction as the lattice main direction M. A leading edge 20’ of a media sheet crosses the weld seam 16” and has a segment of length L'’ where the closest through- holes 18 are blocked by the weld seam. It can be seen that, in this scenario, L’ would be larger than the length L obtained for the opposite inclination of the weld seam.

Inthe situations shown in Fig. 2, the difference between L and L' may not appear to be remarkable, but it must be observed that this length depends also on the position of the leading edge 20 and 20’, respectively, relative to the weld seam, and this position is generally not predictable because it is determined by the timings at which the media sheets are fed onto the belt.

Fig. 3 illustrates, for the two inclinations of the weld seam shown in Fig. 2, a worst-case scenario where the numbers of blocked-through-holes are as large as they can become. In this case, the segment of the leading edge 20 that is not properly attracted to the belt has a length L which is equal to the total number of consecutive through-holes in a row that are blocked by the weld seam 16. Likewise, the leading edge 20’ now has a segment of a length L’ that is not properly attracted to the belt, and it can now be seen that L’ is significantly larger than L. As a consequence, if the media sheet tends to cockle, the leading edge 20’ cannot be prevented from warping upwards over the length L.

The length L and L’, respectively, depends upon an angle a = B + ¢ that is formed between the seam direction S and the lattice main direction M. More precisely, if b is the width of the weld seam, then L is given by: L = b/sin(o) This formula seems to imply that, in order to minimize L, the angle « should be as close as possible to 90°. In practice, however, this is not attainable. If the lattice main direction M would be parallel with the width direction W, then the seam direction S would have to be the longitudinal direction of the belt, which is of course not possible. For a number of practical reasons, the absolute value of the angle B between the seam direction S and the width direction W should be smaller than 45°, preferably smaller than 22,5° and even more preferably only 10° or smaller. One of the reasons is that the elastic modulus of the weld seam 16 is different from the elastic modulus of the rest of the conveyor belt. Since the belt, in operation, will always have a certain tension, it is subject to tension forces in the longitudinal direction A. If the absolute value of the angle p is large, then these forces would have a substantial component in the direction in parallel with the weld seam, and the belt would tend to warp because of different stretching behaviors of the weld seam and the rest of the belt.

On the other hand, if the absolute value of the angle between the lattice main direction and the width direction would be increased, then, at a certain point, which is reached at 30° for this particular lattice, another lattice axis, namely a2, would become the axis that defines the lattice main direction.

Thus, while there are practical limits for selecting the absolute values of the angles 3 and ¢, it can be stated that the sign of these angles does matter. The objective is to make «a as large as possible (in order to bring it closer to 90°). If the seam direction S and the lattice main direction M are inclined in opposite directions, as in Fig. 1, then a is the sum of the absolute values of B and 4, and «a is relative large. In contrast, if both directions are inclined in the same sense relative to the width direction, then the angle a is the difference between the absolute values of 3 and ¢ and is significantly smaller. It is therefore an important feature of the belt disclosed here that the inclinations of the seam direction S and the lattice main direction M relative to the width direction W are opposite to one another. It is important to note that the design that has been proposed here is not limited to the case that the width b of the weld seam is smaller than the spacing d between the lattice axes a1. If the width b of the weld seam is increased and/or the density of the through- holes 18 in the lattice is increased, the number of through-holes 18 that become blocked will become larger, but the length L may still be kept small enough to avoid cockling of the media sheets. Essential steps of a method of manufacturing the conveyor belt 10 have been sketched in Fig. 4. An endless web 10a of a film material that is to form the conveyor belt 10 is supplied in the direction A. The web 10a has been perforated already in a previous manufacturing step. For example, the perforations 18 may be formed by passing the web over a punch roller which has spikes at the intended locations of the through-holes so as to pierce the web at these locations. If the spikes are aligned on the circumferential surface of the punch roller on straight lines in parallel with the axis of the roller, then the angle of inclination of the lattice main axis will be 0. In order to obtain a non-zero angle of inclination, the spikes may be arranged along helical lines that extend both axially and circumferentially over the peripheral surface of the roller.

In a determination stage 24, the lattice main direction W of the perforations in the web 10a is determined.

This can be achieved for example by measuring the locations of the through-holes with an optical device.

As an alternative, the relevant information on the lattice main direction may simply be obtained from the manufacturer of the web 10a.

A cutting device 26 is provided for cutting the web 10a into pieces 10b of a desired length, the cut being performed along a cut line 28 that will determine the seam direction S.

The angular orientation of the cut line 28 relative to the longitudinal direction A of the web is adjustable, and based on the information provided by the determination stage 24, the angle is adjusted such that the seam direction S and the lattice main direction M are inclined in opposite directions relative to the width direction W of the web.

Then, in a subsequent manufacturing step that has not been illustrated here, each piece 10b is folded into a loop such that opposite ends 30, 32 of the piece overlap each other and are welded together so as to form the weld seam 16. Fig. 5 is a longitudinal section of the endless conveyor belt 10 obtained in this way, the belt being trained around two rollers 34 of a belt conveyor and being driven such that the upper run of the belt moves over the suction box 22. A cross section of the weld seam 16 is visible in the upper run of the belt.

Embodiments

1. A conveyor belt (10) for a sheet transport system, wherein the belt has a weld seam (16) extending across the belt in a seam direction (S) inclined relative to a width direction (W) of the belt (10), and the belt has a pattern of through-holes (18) arranged in a regular lattice, the lattice having a number of axes (a1, a2, a3, a4) on which the through-holes (18) are aligned, and having a lattice main direction (M) defined as the direction of the axis (a1) for which a deviation from the width direction (W) is smallest, characterized in that the seam direction (S) and the lattice main direction (M) are oppositely inclined relative to the width direction (W).

2. The conveyor belt according to embodiment 1, wherein the regular lattice is a tessellation of the area of the belt (10) with rhomboids.

3. The conveyor belt according to embodiment 2, wherein each rhomboid is composed of two isosceles triangles.

4. The conveyor belt according to any of the preceding embodiments, wherein an angle (B) of inclination of the seam direction (S) relative to the width direction W is smaller than 22,5°, preferably not larger than 10°.

5. The conveyor belt according to any of the preceding embodiments, wherein the angle (¢) of inclination of the lattice main direction {M) relative to the width direction (W) is smaller than 22,5°, preferably not larger than 10°.

6. The conveyor belt according to any of the preceding embodiments, wherein the weld seam (16) has a width (b) which is larger than a spacing (d) between parallel rows of through-holes (18) that extend in the lattice main direction (M).

7. A method of manufacturing a conveyor belt (10}, the method comprising the steps of: - providing an web material (10a) having a width direction (WW) and having a pattern of through-holes (18) arranged in a regular lattice, the lattice having a number of axes (a1, a2, a3, a4) on which the through-holes (18) are aligned, and having a lattice main direction (M) defined as the direction of the axis (a1) for which a deviation from the width direction (W) is smallest;

- cutting the web (10a) into pieces (10b) along cut lines (28) that are inclined relative to the width direction (W) of the web; and - welding opposite ends (30, 32) of each cut piece (10b) together, thereby to form the endless conveyor belt having a weld seam (16), characterized by the steps of: - first determining the lattice main direction (M) of the web; - and then adjusting a cutting device (26) such that the cut lines (28) and the lattice main direction (M) are oppositely inclined relative to the width direction (W).

Claims

Conclusions

A conveyor belt (10) for a sheet transport system, wherein the belt comprises a weld seam (18) extending across the belt in a seam direction (S) inclined with respect to a width direction (W) of the belt (10), and wherein the band comprises a pattern of perforations (18) arranged in a regular grid, the grid comprising a plurality of axes (a1, a2, a3, a4) on which the perforations (18) are aligned, and comprising a main grid direction (M) , which is defined as the direction of the axis (a1) for which a deviation from the width direction (W) is smallest, characterized in that the seam direction (S) and the main grid direction (M) are oppositely inclined to the width direction (W).

Conveyor belt according to claim 1, wherein the regular grid is a pattern of diamond shapes which substantially fill the surface of the belt (10).

The conveyor belt of claim 2, wherein each diamond shape consists of two isosceles triangles.

Conveyor belt according to one of the preceding claims, wherein an angle (3) of the inclination of the seam direction (S) with respect to the width direction (W) is less than 22.5°, preferably not greater than 10°.

Conveyor belt according to one of the preceding claims, wherein the angle (¢) of the slope of the main grid direction (M) with respect to the width direction (W) is less than 22.5°, preferably not greater than 10°.

Conveyor belt according to one of the preceding claims, wherein the weld seam (16) has a width (b) which is greater than a distance (d) between parallel rows of perforations (18) extending in the main grid direction (M).

A method of forming a conveyor belt (10), the method comprising the steps of: - providing a web material (10a) having a width direction (W) and having a pattern of perforations (18) provided in a regular grid, the grid comprising a number of axes (a1, a2, a3, a4) to which the perforations (18) are aligned, and which have a main grid direction (M) defined as the direction of the axis (a1) for which a deviation from the width direction (W) is the smallest; - cutting the web (10a) into pieces (10b) cut along cutting lines (28) inclined to the width direction (W) of the web; and - welding opposite ends (30, 32) of each piece (10b) together to form an endless conveyor belt with a weld seam (16), characterized by the steps of: - first determining the main grid direction (M) from the web; - and then adjusting a cutting device (28) so that the cutting lines (28) and the main grid direction (M) are oppositely inclined with respect to the width direction (W).